Saute onions in ¼ cup oil on a low flame for at least 20-30 minutes, but longer is even better. You can saute the onions ahead of time.
Prepare the knishes:
Preheat oven to 400.
In a large bowl, combine the caramelized onions, potatoes, oil, eggs, potato starch, salt and pepper, if using.
For best results, break up the potatoes first using a potato masher or a heavy spoon.
Using an electric mixer, blend together all ingredients until mostly smooth. A few lumps are fine. Do not over-mix.
Grease cupcake pans well with oil (a little extra in each pan is well worth the calories - it really helps the knishes develop a fried-like crust). Fill the pans until almost full with potato batter.
Bake at 400 for about 26-28 minutes, until tops are golden brown.
Serve hot.
These knishes freeze well!
Recipe by Overtime Cook at https://overtimecook.com/2015/03/31/doughless-potato-knishes-for-passover/